The nav/display is obviously better in the Tesla (although my Golf didn't have the digital cockpit that they're putting in the new ones). Both cars have their 'fancy' seating material (leather/fake leather/whatever) on the seating surfaces only, cloth elsewhere (and, by the way, I hate leather seats, I just want cloth in everything.. I'm just saying, this is one way premium cars are differentiated, is by FULL leather). The most galling thing to me on the R, the only real sign of cost cutting, was the manual passenger seat, where the 3 has a power seat. A low end touch on both is the totally spartan, stripped out finishing of the trunk/hatch area.
No swiveling headlights on the 3, but the headlights are actually better, significantly so, particularly on high beam.
Perhaps one thing that keeps me from being as critical of the 3 is that it's an appliance to me. I'm a german car fan, and I hate sedans. My BMWs and VWs have been cars I'm passionate about. The Tesla just takes me from Point A to Point B. And it's a fantastic car. But maybe that makes my expectations lower.
Do you miss having the hatchback? That is one my bigger gripes with the M3. This would be my only car.
I love driving the 3, and ours is an RWD LR with the 18" eco crap tires. I can't say I miss driving the R, but I miss the way it looks and having that unique car that I'm passionate about, and I really enjoyed having a manual transmission.
I have a manual sports car as well, but you know what, I always choose the 3 when I need to go run an errand, so maybe that's all you need to know. Just about the only time I've driven my sports car in the past year is 2 track days. Hardly any street miles.
Teslas offer a different USP than E-Tron/I-Pace alikes. It's EV vs. Premium-Cars that happen to be EVs.
If you've never owned a (premium) car and thus have no feeling for differences in interior- and general-manufacturing-quality, a Tesla is the reasonable choice (it even maybe that an Audi's interior will come across as needlessly pretentious).
However, if you've driven premium Audis/Jags you will notice what Teslas are lacking.
It's reasonable to assume that Teslas are thus more likely to be bought by newly affluent millennials (than by already affluent people), though being a TSLA stockholder I wonder how large that group of millennials might be outside of my software engineering bubble.